Intake manifolds of internal combustion engines have conventionally been manufactured by die-cast molding. In recent years, however, intake manifolds manufactured out of a synthetic resin by injection molding have also been proposed in order to make the intake manifolds lighter weight.
Injection molding is a process in which a resin material that has been plasticized by heating is injected within a metal mold at high pressure. The metal mold is pulled off after cooling solidification or heat curing, and a molded piece is obtained. Injection molding has an advantage in that members having a complex shape can be manufactured at a relatively low cost.
JP 9-177624 A and JP 9-195869 A, issued by the Japan Patent Office in 1997, disclose methods in which an intake manifold is divided in half into upper and lower components, and the injection molded components are unified by vibration welding.